Baez-Cotto Carlos M, Jackson Grayson L, Mahanthappa Mahesh K
Department of Chemistry, University of Minnesota, 207 Pleasant St. S. E., Minneapolis, Minnesota 55455, United States.
Department of Chemistry, University of Wisconsin, 1101 University Ave., Madison, Wisconsin 53706, United States.
Langmuir. 2020 Mar 10;36(9):2307-2321. doi: 10.1021/acs.langmuir.9b03408. Epub 2020 Feb 26.
We report detailed small-angle X-ray scattering (SAXS) studies of the impact of variable -decane loadings on the lyotropic liquid crystalline (LLC) phase behaviors of homologous bis(tetramethylammonium) gemini didecanoate surfactants , which derive from dimerizing decanoic acid through its α-carbon with hydrocarbyl linkers -(CH)- where = 3, 4, 5, and 6. amphiphiles with = 3 or 5 exhibit a strong propensity to form normal double gyroid (G) LLC network mesophases over wide surfactant hydration ranges, as compared to homologues with = 4 or 6. On swelling aqueous LLC mesophases with up to 35 wt % -decane, we demonstrate that odd-carbon linked surfactants ( = 3 or 5) form G and normal double diamond (D) phases over wide water concentration windows with = 22-100 °C. Complementary studies of decane-swollen ( = 4 or 6) aqueous LLCs instead demonstrate significantly diminished network phase stability, in favor of hexagonally-packed cylinder phases and a zoo of complex quasispherical micelle packings, which include micellar C14 and C15 Laves phases ( and symmetries, respectively) and high-symmetry hexagonally close packed (HCP) and body-centered cubic (BCC) arrangements. These rich phase behaviors are rationalized in terms of linker length parity-dependent surfactant conformations and the delicate free energy balance that guides the packing of these geometrically anisotropic amphiphiles by minimizing unfavorable water-hydrophobic contacts, maximizing ionic surfactant-headgroup counterion solvation with minimal local variations, and maximizing electrostatic cohesion within these supramolecular assemblies.
我们报告了详细的小角X射线散射（SAXS）研究结果，该研究探讨了可变癸烷负载量对同源双（四甲基铵）双子癸二酸二酯表面活性剂的溶致液晶（LLC）相行为的影响，这些表面活性剂是通过癸酸的α-碳与烃基连接基-(CH)-二聚而成，其中 = 3、4、5和6。与 = 4或6 的同系物相比， = 3或5的两亲物在较宽的表面活性剂水合范围内表现出形成正常双螺旋（G）LLC网络中间相的强烈倾向。在用高达35 wt% 的癸烷溶胀水性LLC中间相时，我们证明奇数碳连接的表面活性剂（ = 3或5）在 = 22 - 100 °C的宽水浓度窗口内形成G相和正常双菱形（D）相。相反，对癸烷溶胀的（ = 4或6）水性LLC的补充研究表明，网络相稳定性显著降低，有利于六方堆积圆柱相和一系列复杂的准球形胶束堆积，其中包括胶束C14和C15 Laves相（分别为和对称）以及高对称六方密堆积（HCP）和体心立方（BCC）排列。这些丰富的相行为可以通过连接基长度奇偶性依赖的表面活性剂构象以及精细的自由能平衡来解释，该平衡通过最小化不利的水-疏水接触、最大化离子表面活性剂头基反离子溶剂化且局部变化最小以及最大化这些超分子聚集体内的静电凝聚来指导这些几何各向异性两亲物的堆积。
